This invention relates to a method for recovering oxalate from solutions containing complexes of iron and chromium, especially solutions resulting from cobalt processing.
In the processing of material to recover cobalt, solutions are generated which contain oxalates and soluble complexes of iron and chromium.
Cobalt is a strategic metal with many important and industrial applications. Because most of the cobalt used in the United States must be imported, the recovery and recycling of cobalt from scrap and other secondary sources is of considerable interest. Cobalt based superalloys typically contain about 40% to 60% cobalt and about 20% chromium. Following digestion of the superalloy in acid, pH adjustment precipitates the chromium and iron values as chromic and ferric hydroxides. Unfortunately, as much as 5% to 30% of the cobalt can be entrained in the gelatinous precipitate. In the processing of material such as this to recover the cobalt, waste solutions are generated which contain oxalate and soluble complexes of iron and chromium. It would be desirable from an economic standpoint to recover the oxalate.
U.S. Pat. No. 4,184,868 relates to a method for producing extra fine cobalt metal powder by digesting cobalt pentammine choride in ammonium hydroxide to obtain a black precipitate which contains cobalt and which is thereafter reduced to metal powder. U.S. Pat. Nos. 4,214,894, 4,233,063, and 4,278,463 relate to improvements in 4,184,868 in which the ammonia solutions are processed to recover any cobalt therein. U.S. Pat. Nos. 4,395,278 and 4,469,505 relate to improvements in 4,184,868 in which fine cobalt metal powder is produced having reduced tailings.
U.S. Pat. No. 4,214,895 relates to a process for producing cobalt metal powder which involves treating an aqueous solution of a soluble cobaltic ammine halide with a sufficient amount of a soluble metallic hydroxide to form a cobalt containing precipitate which is thereafter reduced to metallic cobalt.
U.S. Pat. No. 4,218,240 relates to a method for producing cobalt metal powder by forming a solution of a cobalt hexammine compound and treating the solution with a metallic hydroxide to form a precipitate which is reduced to cobalt metal powder. U.S. Pat. Nos. 4,348,224 and 4,381,937 relate to improvements in the process described in U.S. Pat. No. 4,218,240 which involve removal of copper and silver from the cobalt. U.S. Pat. No. 4,452,633 relates to an improvement in the processes described in U.S. Pat. Nos. 4,218,240 and 4,348,224 in which the silver is recovered.
U.S. Pat. No. 4,093,450 to Doyle et al describes a process for producing fine particle size cobalt metal powder by the hydrogen reduction of cobalt oxide obtained from a cobalt pentammine carbonate solution. The precipitate is formed by heating the solution to drive off ammonia and carbon dioxide to form a precipitate od cobalt oxide. This process requires a solution of about 4 grams of cobalt per liter to produce a metal powder having a particle size of less than about 1 micron. Note that the final resulting particle size of less than about 1 micron is highly dependent on the concentration of cobalt employed in the aqueous solution.
U.S. Pat. No. 4,329,169 relates to a process for producing fine cobalt metal powder absent tailings by heating an aqueous solution of soluble cobalt ammine halide to decompose the halide and form a cobalt containing precipitate which is reduced to the cobalt metal powder.
U.S. Pat. No. 4,409,019 relates to a process for producing fine cobalt metal powder from pieces of relatively pure cobalt by dissolving the cobalt pieces in an aqueous solution of hydrogen iodide and iodine and forming a cobalt containing solid which is subsequently reduced to a fine cobalt metal powder.